Impact of two severe geomagnetic storms on the ionosphere over Indian longitude sector during March-April 2023
by Siva Sai Kumar Rajana, Sampad Kumar Panda, Sridevi Jade, Chiranjeevi G. Vivek, A. K. Upadhayaya, Arti Bhardwaj, Sonam Jorphail & Gopi Krishna Seemala
We investigated the ionosphere response to the two severe geomagnetic storms in the ascending phase of solar cycle 25 which occurred during the 23-24 March 2023 (SYM-Hmin = −169 nT) and 23-24 April 2023 (SYM-Hmin = −233 nT) using a latitudinally aligned dense network of Global Navigation Satellite System (GNSS) receivers, magnetometers, and digisonde along the Indian longitude sector. The significant variations in TEC during the storm’s main and recovery phases are mainly linked to the influence of westward Disturbance Dynamo Electric Fields (DDEFs). During the initial phase of the March 23-24 geomagnetic storm, no changes in daytime TEC were observed, despite the storm occurring at noon time with a southward IMF Bz due to the influence of electron density in the top side ionosphere. Furthermore, both pre-reversal enhancement (PRE) and ionosphere irregularities are suppressed within two hours of their onset during the main phase of the March 23-24 storm, owing to the westward transition of zonal electric fields from an eastward direction. During the recovery phase of both storms, a daytime positive storm effect is observed over the dip equatorial region, while the beyond equatorial ionization anomaly (EIA) and mid-latitude regions perceived a negative ionospheric storm effect. This phenomenon is attributed to the influence of the dominant westward DDEFs during the period. Moreover, these DDEFs effectively inhibited the equinoctial manifestation of PRE effects and post-sunset ionospheric irregularities during the recovery phase of both storms. These findings are further confirmed with supporting information from TEC recorded by Swarm satellites, model-derived ionospheric electric fields, and thermospheric O/N2. The results from this study may advance the understanding of ionospheric response to severe geomagnetic storms under the prevailing westward DDEFs during the dayside recovery phase, complementing the global efforts for more reliable space weather modeling and prediction services.
Impact of the Gannon Superstorm on the Equatorial Ionization Anomaly Dynamics During Its Recovery Phase on 11 May 2024
by K. Shimna, R. K. Archana, C. Vineeth, Gang Lu, T. K. Pant and M. S. M. Vijayan
During the recovery phase of the Gannon Superstorm on 11 May 2024, the thermosphere-ionosphere system experienced dramatic changes marked by an unusual redistribution of plasma density. The peak electron density (Nmax) from Global-scale Observations of the Limb and Disk (GOLD), ground-based Vertical Total Electron Content (VTEC), and topside VTEC from Swarm C satellite revealed an enhanced electron density at the equator and a complete disappearance of the Equatorial Ionization Anomaly (EIA) crests. This absence of EIA crests was linked to a strong daytime Counter Electrojet (CEJ) caused by disturbance dynamo effects observed in ground magnetic data. The unusually strong CEJ suppressed the ExB vertical drift, thereby eliminating the fountain effect. Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) simulations further indicated the presence of equatorward converging meridional winds from both hemispheres. This converging wind hindered the diffusion of plasma from the dip equatorial rΣO/N2 ratio along the equator was observed during the recovery phase, further contributing to this phenomenon. The present study, therefore, for the first time, demonstrates the combined effects of storm-induced changes in equatorial electrodynamics, meridional winds, and significant compositional changes during the recovery phase of a superstorm, and their influence on plasma distributions. The corroborative evidence from model simulations further strengthened these observational findings.
Impact of land-use changes on the genesis and evolution of extreme rainfall event: a case study over Uttarakhand, India
by S K Sahoo, Ajilesh P P, K C Gouda & Himesh S
Abstract
This study is about the impact assessment of different land-use data sets on the simulation of an Extreme Rainfall Event (ERE) which is one of the unusually rare events that occurred between 14th to 18th of June 2013 over Uttarakhand in India. In this work, high-resolution (2-km), time ensemble simulations are carried out using Weather Research and Forecasting model (WRFV3.5) with a 3-nest configuration. The sensitivity analysis of the model in simulating rainfall to different land-use data i.e. USGS-24 category (1992–93), ISRO (2004–05) and (2012–13) are carried out. Comparison of simulated rainfall which is averaged over the study region with that of IMD observed station data (averaged over 23 stations) showed that the simulations based on ISRO land-use data are comparatively more accurate with lesser simulation error when compared to simulations with USGS land-use data. The percentage of error in rainfall for the 3 simulations was found to be 24% (USGS), 9.5% (ISRO-2005) and 10% (ISRO-2013) with respect to the IMD observation. During the initial stage, the results have shown maximum convergence and vorticity with a strong updraft. The strong updraft, however, persisted throughout the simulation period. The increasing tendency of positive vorticity both in the simulation and observation suggests an intensification of cyclonic circulation in a vertical direction and hence creates instability in the boundary layer causing ERE over Uttarakhand. This study shows that ISRO land-use data is a relatively more realistic representation of the study region than the USGS data, and found to be useful in reducing the model error in the simulation of such rare events over this kind of mountainous region.
Source: https://link.springer.com/article/10.1007/s00704-020-03129-z
Impact of different land use data on WRF model short range forecasts during pre-monsoon and monsoon seasons in India
by P. Ipsita, V. Rakesh, Randhir Singh and G.N. Mohapatra
Abstract
This study focuses to analyse the impact of land use changes on short range weather forecasts over Indian region. Weather Research and Forecasting (WRF) model simulation experiments are conducted by using land use data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Indian Space Research Organization (ISRO) satellites for pre-monsoon and monsoon season. MODIS 2001 land use is used in control (CNT) experiment and updated land use with recent urban class from MODIS (EXP1) and ISRO (EXP2) for the year 2019 is used to generate model lower boundary conditions in other two experiments. Quantitative error measures and skill score computed for rainfall forecast showed that model skill is better with the use of realistic recent land use data from MODIS and ISRO during pre-monsoon and monsoon period. Extreme Dependency Index score computed also revealed that model skill in predicting extreme rare rainfall events is improved with recent landuse data. Model simulated surface meteorological variables and profiles at lower levels also found to be improved with the inclusion of realistic land use class from MODIS and ISRO. Between the two experiments, the one which used ISRO based land use showed larger improvement particularly during the monsoon season.
Source: https://doi.org/10.1016/j.uclim.2023.101558
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